The present invention generally relates to the covering of bulk salt piles stored outdoors. More particularly, the invention relates to covering bulk salt piles or mounds which are stored outside or outdoors where the salt is waiting to be spread as a deicing composition and where the cover for the salt is a foamed concrete which will easily break up into particulate matter which will spread along with the deicing composition.
Millions of tons of deicer salt in the form of sodium chloride, calcium chloride and magnesium chloride is applied in many countries to roads, bridges and sidewalks during the cold winter season to melt ice and snow. Sodium chloride is most commonly used, but all of these salts have to be stored and be ready for transport and spreading at indeterminate times depending upon the weather. Storing deicing salts, such as sodium chloride, outdoors exposed to the elements, however, creates problems. Rain and snow will wet the salt which will solubilize to some extent and then form a hard crust which will cause spreading problems. Rain, snow and wind also will erode the piles. This causes several problems.
The salt pile will spread and require more area for storage. Also the water from the rain and snow will solubilize a portion of the salt and it will be lost as a part of a brine type of run off. But even more important, the aqueous solution of salt which forms the run off is an environmental problem which can contaminate surface water and ground water and will be detrimental to surrounding vegetation.
To solve the aforedescribed problems salt piles have been covered with tarpaulins. In some cases, structures have been built to house the salt, such as xe2x80x9cbeehivexe2x80x9d shaped structures often seen by the roadsides in the northern American Midwest. These solutions, however, are not without drawbacks. The tarpaulins are expensive, heavy and difficult to move. They are also subject to inadvertent ripping and tearing by earth moving equipment loading salt onto spreader trucks. The structures used to house salt are expensive and also prone to inadvertent damage during the movement of the bulk salt.
It is an object of this invention to provide an easy way to cover bulk salt stored outdoors so that it will be protected from rain, snow and wind.
It is an object of this invention to reduce brine run-off from bulk salt stored outdoors.
It is yet another object of this invention to provide a cover for a bulk salt pile or mound that will retain the integrity of the salt pile or mound.
These and other objects, advantages, features and characteristics of the present invention will become more apparent upon consideration of the following description and appended claims.
The present invention is directed to a foamed composition and method for forming an inexpensive, semi-permanent cover layer over deicing salt which is stored outdoors in large bulk mounds or piles. The cured foamed cover layer protects the salt from moisture, wind and other erosive elements so that the salt can be stored outdoors for extended periods of time without experiencing agglomeration of the salt particles from moisture, erosion or deterioration of the salt mound and without experiencing the deteriorating effects of the elements. The cured foamed cover layer protects the salt by forming a continuous coating over the exposed surface of the salt mound or pile and eliminates or substantially eliminates brine water run off from the pile that would otherwise occur as a result of moisture from the elements solubilizing and then transporting dispersed or solubilized salt from the bulk salt pile. Moreover, the invention has the additional advantage of allowing easy recovery of the salt after some of the salt pile has been removed. As it becomes desirable to remove a volume of salt from beneath the cured foamed cover layer, a portion of the cover layer may be broken and removed as necessary to expose the salt and provide access for its removal. In this way, the remaining portion of the cover layer may be left on the salt until it is desired to remove more of the salt. A cover layer then may be reapplied to cover any areas of the salt pile that are exposed as a result of removing salt from the pile.
Broadly, the cured foamed cover layer formed by the method of the invention comprises cured cement, and in an important aspect, cured concrete which has been foamed with a foaming agent, without any other organic polymeric material which will form a polymeric coating or layer except an optional water resistant/repellant additive. The cured foamed cover layer, which provides a water resistant foamed coating over the salt mound, is of a thickness which is effective for maintaining the integrity of the salt mound for at least a year when exposed to the outdoor elements and which is effective for minimizing passage of moisture to the salt for at least that time. The cured foamed cover composition is brittle and readily broken into particulates which can be spread with the particulate salt, but the cured cover or layer is effective for providing a cover layer over the salt that is a continuous, hardened coating which generally protects the salt from water and keeps the integrity of the mound or pile of bulk salt comprising sodium chloride, calcium chloride, magnesium chloride and mixtures thereof. The cured foamed cover has a density of not more than about 1.6 gram/cm3, and in an important aspect, it has a density in the range of from about 1.4 to about 0.9 gram/cm3 and a strength in the range of from about 28 to about 8 as measured on a Ametex-Accru-Force Cadet Force Gauge as available from Ametek using 0.5 cm chisel.
The cured foamed cover composition is entirely compatible with the end use of the deicing salt. As the deicing salt is used, an amount of the cured cover will be crushed and intermixed with the salt without deleterious effect to the salt. Indeed, the crushed cover will enhance some aspects of the use of the deicing salt because its particles will enhance traction over ice and snow.
In an important aspect, the method of the invention includes applying a foamed cover composition which in its cured form comprises a blend of foaming composition, aggregate, cement and water on the salt mound (especially sodium chloride in the form of rock salt). The cured foamed cover composition comprises from about 2 to about 14 weight percent cement, based upon the weight of the cement, aggregate and other solid components. The amounts of foaming composition, aggregate and water in the uncured foamed cover composition are effective to provide the cured foamed cover composition with a density of from about 1.6 to about 0.9 gr/cm3 and a strength of from about 28 to 8. The aggregate also should not be too fine (not greater than about 10 U.S. standard mesh) to assure that the cover will not be too hard and stay brittle so that the salt can be readily accessed without damage to moving equipment such as front loaders. Larger aggregate causes the concrete to break too easily since the aggregate dimensions will approach or exceed the thickness of the concrete layer. Also keeping the size of the aggregate to not greater than 10 mesh, but not less than 300 mesh (except for fly ash which could have a particle size which is finer than 300 mesh), provides a cover which can be reduced to particulates which are in a size such they can be spread with spreader equipment along with the salt on surfaces with ice and snow. In an important aspect the aggregate is selected from the group consisting of sand, fly ash, silica and mixtures thereof. In general, the cured foamed cover composition will comprise from about 2 to about 14 weight percent cement, from about 97.6 to about 70 weight percent aggregate and from about 0.4 to about 6 weight percent foaming composition.
In an important aspect, the pile or mound of salt is permitted to shift or settle, such as from about 3 to about 7 days before the foamed cover composition is applied to the salt. Thereafter, the foamed cover composition is applied directly to the exposed surface of the salt with an eductor nozzle, hydraulic pump or other conveying equipment. The foamed cover composition is applied in an amount which is effective for maintaining the integrity of the salt mound for at least about one year when exposed to the outdoor elements and which is effective for minimizing passage of moisture to the salt for at least that time, which as a wet slurry is generally, about 1 to about 12 pounds of composition per square foot of the surface of the salt (or 0.5 to about 12 pounds as a dry composition).
To maintain the integrity of the salt pile as aforesaid, the foamed cover composition should be applied to the surface of the salt mound in an amount which is effective for providing a cured layer having a thickness of from about 0.1 to about 1.0 inch, and in an important aspect about 0.5 inch. The aqueous blend which is the foamed cover composition is sprayed onto the salt pile in order to form a solid, essentially impermeable cover layer of foamed concrete after curing. The amount of water used to apply the foamed cover composition should be effective to permit a hydraulic pump and/or an eductor to spread that composition and provide the density and strength described above. The thickness of the cover layer should generally be from about 0.1 to about 1.0 inch, and as noted above, in an important aspect about 0.5 inch. Prior to spraying the foamed cover composition onto the salt, the dry components of the foamed cover composition are mixed with the water and foaming agent to provide an aqueous foamed cover composition which then is sprayed as a slurry over the exposed surface of the salt.
As used herein, xe2x80x9ccementxe2x80x9d means any inorganic substance that is capable of setting and hardening with water, as a result of the interaction of water with the constituents of the substance, to act as a bonding agent for materials. By xe2x80x9ccementxe2x80x9d is meant to include the class of hydratable or hydraulic cements such as Portland cement, sorrel cement, calcium-aluminate cement, magnesia cement, gypsum cement and mason""s cement.
As used herein, xe2x80x9chydratable cementxe2x80x9d or xe2x80x9chydraulic cementxe2x80x9d means self-curing cements which cure with water of hydration such as Sorrel cement, Portland Cement, Pozzolan cement and calcium aluminate cement.
As used herein, xe2x80x9cPortland cementxe2x80x9d means a mixture of limestone silica and clays which is calcined and then mixed with gypsum.
As used herein, xe2x80x9cSorrel cementxe2x80x9d means a hydrated combination of MgCl2 and MgO, MgSO4 and MgO or MgCl2 or MgSO4. The ratio of MgCl2 or MgSO4 to MgO in Sorrel cement broadly is about 1:1 to about 1:30 (or 1:0.42 to 1:1:13 weight ratio). Sorrel cement can include a combination of MgCl2, MgSO4 and MgO with the MgSO4 being at least partially interchangeable with MgCl2.
As used herein, xe2x80x9ccalcined gypsumxe2x80x9d means CaSO4.xc2xdH2O and CaSO4 in the form of Keene""s cement which when combined with water, hydrates and forms hydrated gypsum or gypsum cement.
As used herein, xe2x80x9cconcretexe2x80x9d means a cementitious substance which is a mixture of cement, aggregate and water, and optionally, any additives, such as a drying enhancer or water repellant.
As used herein, xe2x80x9caggregatexe2x80x9d means fly ash, sand, silica and any material derived from rock or manufactured from clays, shales, slates and slags.
As used herein, xe2x80x9cwater repellentxe2x80x9d means any material that reduces the cover layer""s permeability to and absorption of water.
As used herein, xe2x80x9cwater resistantxe2x80x9d means the ability to repel water so as to minimize the passage of water therethrough.
The invention includes a salt mound having a water resistant cover layer comprising a cured foamed cover composition, a method for providing the foamed cover composition and covered salt piles and both the cured cover as well as the foamed cover composition (prior to curing). The cured foamed cover composition is a cementitious composition comprising cement, foaming composition and aggregate where the cover after curing has a thickness which is effective for maintaining the integrity of the salt mound for at least a year when exposed to outdoor elements and which is effective for minimizing passage of moisture to the salt for at least one year. The cured layer of foamed concrete generally will have a thickness of from about 0.1 to about 1.0 inch which will require that from about 0.5 to about 12 pounds of dry composition is applied to every square foot of salt surface.
The foamed cover composition has sufficient water to permit it to be spread by a hydraulic pump and/or an eductor and to permit it to cure into a solid, essentially impermeable, cover layer of cement or concrete.
Any foaming composition compatible with permitting the cement curing into a hardened cover may be used. Foaming agents include cationic surfactants, alkyl olefin sulfonates, alkali metal salts of alkyl ether sulfates, such as a sodium salt of an alkyl ether sulfate, and sodium lauryl sulfate.
The cured foamed cover composition which is applied to the salt pile comprises from about 2 to about 14 weight percent cement and amounts of foaming composition and aggregate which are effective for providing a cured foamed cover which has a density and a strength as previously described. Generally prior to curing, the uncured foamed cover composition will comprise from about 1 to about 12 weight percent cement, from about 0.2 to about 4 weight percent foaming composition, from about 54 to about 78 weight percent aggregate (based on the weights of cement, foaming composition and aggregate) and the remainder water.
In an important aspect, to increase water resistance of the cured cover layer, a water resistant additive also can be mixed with the aqueous foamed composition before it is applied to the salt mound. Alternatively, the water resistant additive composition may be applied over the cover layer after application of the aqueous foamed composition in an amount effective for providing water resistance to the surface of the cured salt cover. In general the water resistant additive when applied with the uncured foamed cover composition may comprise from about 0.3 to about 15 weight percent, based upon the weight of the dry cementitious composition. Any water resistant additive compatible with curing the foamed cover composition, or mixtures thereof, which are known to those skilled in the art can be used. Suitable additives include latexes available as Darex 526L (carboxylated styrene butadiene vinylidene chloride polymer); Versaflex 9 (vinylidene chloride butyl acrylate polymer); Daratak xb3631 (polyvinylidene chloride terpolymer); Darex (styrene butadiene itaconic acid polymer); Versaflex 1 (vinyl acetate butylacrylate-vinyl versate polymer); and Everflex GT (hexylene glycol vinyl acetate dibutylmaleate copolymer vinyl acetate monomer). The water resistant additives also may include soaps of fatty acids (such as alkali or alkaline metal salts of fatty acids) or fatty acids such as oleic acid, sodium oleate, calcium oleate, stearic acid; sodium stearate or calcium stearate. Aggregate materials such as fly ash and silica, such as silica available as Microsilica EMS 965 by Elkem Materials Inc. or Fumed Silica Aerosil R 972 by Degussa Corp. also may provide some water resistance. Other commercial additives may be used such as DAP Water Stop and Plug by D.A.P. Inc. and Akona Cement Waterproofer #1625 (Akona, Inc., 1570 Halfrin Road, Maple Plain, Minn. 55359). These suitable water-proofing solutions also may be sprayed onto the cured foamed cover to enhance the water resistant effect of the cover layer.
In yet another aspect, the foamed cover composition may include an accelerator to provide a quick curing cover layer. Calcium aluminum cement is a suitable accelerator and may be included in the dry component of the foamed cover composition in an amount of from about 1 weight percent to about 20 weight percent based upon the weight of the dry components composition.
According to the method of the invention, it is important that the salt mound be permitted to settle and shift for about three to seven days after the salt pile is created and before the cementitious composition is applied to the pile or mound. The foamed cover composition may be applied by an eductor sprayer with the sprayer being operated from a moveable xe2x80x9ccherry pickerxe2x80x9d whereby an operator would aim a spray of the concrete over the bulk salt. Alternatively the foamed cover composition may be applied using a hydraulic pump with commercially available nozzles.
The following examples illustrate the invention and the method of the invention and should be understood to be illustrative of, but not limiting, upon the scope of the invention which is defined in the claims.